1. Field
The present disclosure relates generally to communication systems, and more particularly, to light emitting diodes (LEDs) forward voltage measurement for optimum system efficiency.
2. Background
LEDs are used as status indicators and displays on a wide variety of equipment and installations because of their low energy consumption, low maintenance and small size. LEDs are used in large-area displays in stadiums, as decorative displays, in traffic lights, and at airports and and railway stations for destination displays. LEDs may also be used in portable devices such as mobile phones.
The current and voltage characteristics of LEDs are similar to other diodes, in that the current depends exponentially on the voltage. This means that a small change in voltage may cause a large change in current. As a result, LEDs are not controlled by voltage alone and need a constant current source or a current limiter in series with the supply. If the supply voltage is not sufficient for the current source and the forward voltage of the LED, there is a significant current roll-off in the LEDs which is not desirable from a user's point of view. The measurement of the forward voltage of the LED can be used to prevent this current roll off. This measurement should be coupled with a system power converter that provides optimum supply voltage while maintaining the desired performance from the LED.
As cell phones and other personal devices gain more functionality more LEDs are used to indicate the status of functions and other operations. One aspect of LEDs is that the amount of voltage needed for optimum system efficiency changes over time. Another aspect particular indicator LEDs is that the forward voltage shows significant variation from part to part. In every LED driver, headroom is needed to avoid current roll-off. When the battery voltage drops, the power source may be switched to a higher boost power supply. In order to achieve the greatest system power efficiency, the threshold needs to be set as low as possible while still meeting the necessary headroom limits.
There is a need in the art for adaptively achieving the lowest headroom necessary while still providing desired current to the LEDs. The adaptive methodology provided accounts for any variation in the LED forward voltage due to process, temperature, aging, and other factors of usage in the given application